Vagus nerve stimulation: predictors of seizure freedom

Abstract

Objectives: To identify predictive factors for the seizure-free outcome of vagus nerve stimulation (VNS). Methods: All 47 patients who had undergone VNS implantation at one centre and had at least one year of follow up were studied. They underwent complete presurgical evaluation including detailed clinical history, magnetic resonance imaging, and long term video-EEG with ictal and interictal recordings. After implantation, adjustment of stimulation parameters and concomitant antiepileptic drugs were at the discretion of the treating physician. Results: Mean (SD) age of the patients was 22.7 (11.6) years (range 7 to 53). Six patients (13%) became seizure-free after the VNS implantation. Only two variables showed a significant association with the seizure-free outcome: absence of bilateral interictal epileptiform discharges (IED) and presence of malformation of cortical development (MCD). Epilepsy duration showed a non-significant trend towards a negative association with outcome. By logistic regression analysis, only absence of bilateral IED correlated independently with successful VNS treatment (p,0.01, odds ratio = 29.2 (95% confidence interval, 2.4 to 353)). Bilateral IED (independent or bilateral synchronous) was found in one of six seizure-free patients and in 33 of 41 non-seizure-free patients. When bilateral IED were absent, the sensitivity for seizure-free outcome was 0.83 (0.44 to 0.97), and the specificity was 0.80 (0.66 to 0.90). Conclusions: Bilateral IED was independently associated with the outcome of VNS. These results are preliminary because they were based on a small patient population. They may facilitate prospective VNS studies enrolling larger numbers of patients to confirm the results. V agus nerve stimulation (VNS) has been shown to be effective treatment for drug resistant epilepsy in two randomised, double blind studies.1 2 During recent years VNS has become an accepted method of treating patients with refractory epilepsy who are not candidates for epilepsy surgery or in whom surgery resulted in no benefit. From the experience of centres using VNS, one third of patients have a reduction in seizure frequency of at least 50%, another third have a worthwhile seizure reduction, while in the remaining third there is little or no effect.3 There is only limited information on patients who become seizure-free. 3 The rate of seizure freedom shows a large variation across the studies which have provided any information at all about it, and ranged from 0% to 24%. [4][5][6][7][8][9][10][11][12][13] Despite increasing amounts of clinical data, it is still not possible to predict which patients will profit from VNS. 14 Determining prognostic factors is important in predicting seizure outcome of VNS and in counselling patients. Moreover, because of the invasive nature of the procedure, the possible hazards of chronic implantation, and the relatively high cost of the treatment, factors indicating a poor prognosis could favour other treatment options including the newer antiepileptic drugs, palliative e...

Vagal nerve stimulation for the treatment of medically refractory epilepsy: a review of the current literature

“…Four studies additionally included data on the percentage of patients achieving freedom from seizures, typically quoted at the 1-year time frame. 9,15,19,28 Of these studies, seizure freedom was reported at a mean of 14.0% (range 9%-27%). …”

“…This volume of information has been used to establish trends in outcome not otherwise evident in investigations with smaller sample sizes. Focal epileptogenic foci and the presence of cortical malformations have been shown to be positive predictors of success with VNS treatment by multiple investigators, including Elliott et al, 10,11 Janszky et al, 19 and Ghaemi et al, 15 but the issue of most appropriate age of implantation appears to remain subject to argument. Ghaemi et al found younger age at initiation of treatment to be a positive predictor, whereas both Elliott et al and Murphy et al found no statistical correlation between younger age and positive outcome.…”

“…On multivariate analysis, 3 factors were found to independently correlate with successful VNS treatment: age at implantation, cortical dysgenesis, and unilateral interictal epileptiform discharges. Janszky et al 19 similarly presented data obtained in 47 consecutive patients with a minimum of 1 year of followup. They were able to demonstrate a 13% rate of seizure freedom, with 2 variables found to significantly predict this freedom.…”

Predicting success of vagus nerve stimulation (VNS) from EEG symmetry

“…Despite the growing application of VNS, it is still not possible to predict which patients respond to what extent to VNS therapy. Most studies that attempt to predict the success of VNS are based upon patient characteristics [4], epilepsy syndrome [5] or localization of the seizure focus [2,6,7]. A meta-analysis by Englot et al on predictors of response to VNS therapy, showed that young patients (<6 years) respond slightly better in terms of seizure reduction compared to adults [2].…”

Invazív neuromoduláció a gyógyszerrezisztens epilepsziák kezelésében

“…A kezdeti klinikai obszervációs vizsgálatok alapján az epilepsziaszindrómák többségében hatékonynak bizonyult [26]. Egy 47 beteg adatainak elemzésén alapuló vizsgálat szerint a jó rohamkimenetel prediktorának a corticalis malformatio és bilateralis EEG-eltérések hiányát találták VNS-implantáció után [27]. Ennek némileg ellentmond az a megfi gyelés, hogy Lennox-Gastaut-szindrómában és az abban jelleg-zetes tónusos axiális rohamokban nagyobb hatékonysá-got mértek [28].…”